Hydrogen Bond Types and Significance - UNSOLVED PRACTICE SET
Chapter: Chemical Bonding and Molecular Structure | Topic: Hydrogen Bond Types and Significance
HYDROGEN BOND TYPES AND SIGNIFICANCE - UNSOLVED PRACTICE SET
Topic: Hydrogen Bond Types and Significance
Multiple Choice Questions
Q1. A hydrogen bond is formed when hydrogen is covalently bonded to:
- Any non-metal
- A highly electronegative atom like F, O, or N
- A metal
- A noble gas
Q2. Which of the following has the strongest hydrogen bonding?
- NH₃
- H₂O
- HF
- CH₄
Q3. Intermolecular hydrogen bonding is responsible for:
- The high boiling point of water
- The linear shape of CO₂
- The ionic nature of NaCl
- The non-polarity of CCl₄
Q4. Intramolecular hydrogen bonding is found in:
- Water
- Hydrogen fluoride
- o-Nitrophenol
- Ammonia
Q5. The zig-zag structure of ice is due to:
- Covalent bonding
- Ionic bonding
- Intermolecular hydrogen bonding
- Metallic bonding
Q6. Which of the following does NOT exhibit hydrogen bonding?
- CH₃OH
- CH₃OCH₃
- HCOOH
- NH₂CONH₂
Short Answer Questions
Q7. Define hydrogen bond. What are the conditions necessary for hydrogen bond formation?
Q8. Distinguish between intermolecular and intramolecular hydrogen bonding with one example of each
Q9. Why does water have a higher boiling point than hydrogen sulphide (H₂S), even though H₂S has a higher molecular mass?
Q10. Explain why ice floats on water. What does this tell you about the structure of ice?
Q11. Your grandmother stores water in a clay matka (earthen pot) during summer. The water stays cool because some of it evaporates through the tiny pores, and evaporation requires energy. But she also tells you that water in a metal container doesn't feel as cool. How does hydrogen bonding in water make evaporation a cooling process, and why does this matter more than the container material?
Q12. Why is the boiling point of HF (19.5°C) lower than that of water (100°C), even though HF forms stronger hydrogen bonds individually?
Long Answer Questions
Q13. Explain hydrogen bonding in detail. Describe:
(a) The conditions required for hydrogen bond formation
(b) The nature of hydrogen bond (electrostatic or covalent character)
(c) Intermolecular hydrogen bonding with examples (H₂O, HF, NH₃)
(d) Intramolecular hydrogen bonding with examples (o-nitrophenol, salicylaldehyde)
Discuss the effect of hydrogen bonding on physical properties like boiling point, viscosity, and solubility.
Q14. Describe the significance of hydrogen bonding in biological systems and everyday life. Explain the role of hydrogen bonds in:
(a) The double helix structure of DNA
(b) The secondary structure of proteins (alpha-helix and beta-pleated sheet)
(c) The high specific heat capacity of water and its importance for climate regulation
(d) The solubility of glucose and other biomolecules in water
Why is hydrogen bonding called the "bond of life"?
Q15. During a science exhibition, your team creates a display on "Hydrogen Bonding in Daily Life."
(a) You demonstrate that a needle carefully placed on water floats, but it sinks when detergent is added. Explain how surface tension, caused by hydrogen bonding, keeps the needle afloat and why detergent disrupts this.
(b) Another exhibit shows that wet clothes dry faster on a windy day. Explain the role of hydrogen bonding in water evaporation and how wind speeds up this process.
(c) Your teammate presents two beakers — one with water and one with ether (C₂H₅OC₂H₅). She drops a crystal of iodine in each. The iodine dissolves in ether but not in water. Explain using the concept of hydrogen bonding and "like dissolves like."
(d) A visitor asks: "If hydrogen bonds are so weak (about 5-30 kJ/mol) compared to covalent bonds (about 400 kJ/mol), why do they matter so much?" How would you answer, citing specific examples?
Numerical / Application-Based Problems
Q16. The boiling points of Group 16 hydrides are:
H₂O: 100°C
H₂S: −60°C
H₂Se: −41°C
H₂Te: −2°C
(a) Plot a graph of boiling point vs. molecular mass for these hydrides.
(b) Explain why H₂O is an anomaly in this trend.
(c) Calculate the energy required to break all hydrogen bonds in 18 g of water if the average hydrogen bond energy is 20 kJ/mol. Assume each water molecule forms 2 hydrogen bonds on average.
(d) If hydrogen bonds did not exist, predict the approximate boiling point of water based on the trend of other hydrides.
Q(3 marks)
17. The following data compares properties of ethanol (C₂H₅OH) and dimethyl ether (CH₃OCH₃), both with formula C₂H₆O:
| Property | Ethanol | Dimethyl Ether |
|---|---|---|
| Boiling point | 78°C | −24°C |
| Solubility in water | Miscible | Sparingly soluble |
| Viscosity | High | Low |
(a) Explain the large difference in boiling points using hydrogen bonding concepts.
(b) Explain why ethanol is miscible with water but dimethyl ether is not.
(c) The enthalpy of vaporization of ethanol is 38.6 kJ/mol, while that of dimethyl ether is 18.5 kJ/mol. Calculate the extra energy due to hydrogen bonding in ethanol.
(d) If you have 46 g of ethanol, calculate the energy required to vaporize it completely.
Q18.5 kJ/mol. Calculate the extra energy due to hydrogen bonding in ethanol.
(d) If you have 46 g of ethanol, calculate the energy required to vaporize it completely.
(3 marks)
18. DNA base pairs are held together by hydrogen bonds:
Adenine-Thymine (A-T): 2 hydrogen bonds
Guanine-Cytosine (G-C): 3 hydrogen bonds
(a) A segment of DNA has 1000 base pairs, with 40% being A-T pairs. Calculate the total number of hydrogen bonds in this segment.
(b) If the DNA strand separates during replication and requires 10 kJ/mol to break each hydrogen bond, calculate the total energy required to separate all base pairs in this segment.
(c) Explain why regions of DNA with more G-C pairs are harder to separate (higher melting temperature) than regions with more A-T pairs.
(d) In proteins, the alpha-helix is stabilized by hydrogen bonds between the C=O of one amino acid and the N-H of another, four residues away. If an alpha-helix has 20 amino acids, how many such hydrogen bonds stabilize the structure?